UK details flu, invasive bacteria co-infections

Feb 4, 2011 (CIDRAP News) – A surveillance report from the United Kingdom yesterday confirmed earlier anecdotal reports of an increase in invasive bacterial infections in flu patients, noting that the spike was most notable for Streptococcus pyogenes, particularly in young adults.

The experts from Britain's Health Protection Agency (HPA) and the European Centre for Disease Prevention and Control (ECDC) published a report on the increase in streptococcal pneumonia in yesterday's issue of Eurosurveillance. The same issue includes a case series of 19 British patients who had invasive group A streptococcal co-infections, which revealed an uncommon influenza B pattern.

After clinicians reported what appeared to be a rise in invasive bacterial infections in flu patients, UK health officials warned general practitioners to be vigilant about a rise in "significiant" bacterial co-infections with influenza and said they would monitor the situation closely to determine if flu was contributing to a rise in bacterial infections.

The infections triggered an analysis of lab isolates and a comparison with past seasons' trends. In yesterday's report HPA experts said S pyogenes and S pneumoniae infections were above expected levels and that heavy flu activity was likely contributing to co-infections in children and young adults.

To gauge the importance of flu as a risk factor for invasive bacterial infection, they matched invasive bacterial surveillance between Nov 1, 2010, and Jan 14, 2011, to lab-confirmed flu diagnoses. Cases with sample dates within 2 weeks of each other were considered possible co-infections.

Comparison to the same period over the past 3 years didn't show an overall increase this season in the number of invasive S pneumoniae, S aureus, Haemophilus influenzae, or Neisseria meningitidis,. It did, however, show a slight elevation in S pyogenes infections, especially in December 2010, when the HPA received 173 reports, compared with an average 99 reports for that period.

While increases in S pyogenes infections were seen across all age-groups and in most regions of England, an increase in S pneumoniae was seen only in young adults ages 15 to 44, at levels much higher for December 2010 than in the previous 3 years.

Of 4,232 invasive bacterial infection reports since the beginning of this flu season, 144 (3.4%) had flu co-infections, the HPA group found. Most of the co-infections were diagnosed within 7 days of the flu confirmation. About three fourths of the co-infections involved influenza A, about a quarter were influenza B, and 2% involved both flu types.

People younger than 44 had the highest likelihood of S pyogenes co-infections. The highest proportion of S pneuomoniae co-infections occurred in those ages 15 through 44.

Though rates of invasive S pyogenes co-infections were higher than expected, case fatality rates for all pathogens were in normal ranges, they reported.

They didn't see a rise in invasive bacteria infections in the youngest children, perhaps because of the introduction of the 7-valent conjugate pneumococcal vaccine in this age in children in 2006 and the transition to the 13-valent version in 2010.

The increase in S pyogenes infections could be related to other factors, such as the weather, the HPA added, pointing out that rates were also higher in older age-groups that weren't as hard hit by flu.

In the other Eurosurveillance report, HPA researchers reported on 19 invasive group A streptococcal (iGAS) infections that were reported in the HPA's Thames Valley unit, located in the southeastern part of the country, from Dec 1, 2010, through Jan 15. The rise in iGAS infections there mirrored a rise across the rest of England.

Six of 10 swabs taken from iGAS patients in the series were positive for influenza: 4 with influenza B, 1 with 2009 H1N1, and 1 with metapneumovirus. None of the patients with confirmed co-infections had received the seasonal flu vaccine. Three of the four patients who were co-infected with influenza B died. The age range was 10 to 47 years, and all were previously healthy.

The group noted that co-infections with S pyogenes, a member of the iGAS group, are uncommon, and reports of co-infections with influenza B are also unusual, especially because the virus is thought o be less pathogenic than influenza A.

They said the findings were striking, especially given the dominance of the 2009 H1N1 virus during most of Britain's flu season, and they added that the results show that influenza B can be lethal in an iGAS co-infection setting.

See also:

Feb 3 Eurosurveillance report on increased S pyogenes and S pneumoniae infections

Feb 3 Eurosurveillance groups A streptococcal infection case series

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